The present invention relates to a method of assessing the amplitude decay of a magnetic storage medium and in particular to a method of calculating an amplitude decay rate of a magnetic storage medium. The invention finds particular application in measuring the amplitude decay of a disc drive.
Currently, the areal density of disc drives is increasing at a rate of more than 50% annually. As areal densities increase, the signal to noise ratio (SNR) of the medium needs to improve so that the bit error rate of disc drives can be maintained. In order to obtain a better signal to noise ratio for the storage medium, the grain size of the magnetic medium is reduced. Unfortunately, as the grain size becomes smaller, the grains become magnetically unstable due to a superparamagnetic effect. This superparamagnetic effect, which is time and temperature dependent, will eventually prevent the medium from being able to retain stored data accurately. As a consequence, there is amplitude loss in the read back signal which causes a degradation in bit error rate. Thus, it is important to measure the rate at which the amplitude of the disc drive will decay over time.
Currently, the decay rate of the drive is measured by repeatedly writing a test track to a magnetic storage medium and measuring how the amplitude of the test track decays over time. However, this process takes an inconveniently long time, typically in terms of days or weeks. Therefore, it would be advantageous to provide a faster method of assessing the amplitude decay rate.
Accordingly, embodiments of the invention provide a method of obtaining an amplitude decay rate of a magnetic storage medium including steps of:
(a) writing a test track to the magnetic storage medium and measuring the initial amplitude of the test track to obtain a reference amplitude;
(b) performing a direct current (DC) erase on the test track using a small write current;
(c) measuring and storing the test track amplitude after step (b) together with a time at which the measurement was made;
(d) writing a reference track;
(e) measuring and storing the reference track amplitude after step (d);
(f) repeating steps (b) to (e) until a DC erase amplitude decay rate has been established; and
(g) calculating a normal amplitude decay rate for the magnetic storage medium from the DC erase amplitude decay rate.
Embodiments of the invention also provide a method of accelerating the amplitude decay of a test track of a magnetic storage medium involving:
(a) writing a test track;
(b) performing a DC erase on the test track; and
(c) repeating step (b) to accelerate the amplitude decay of the test track.